The present invention relates to a transducer for a noise-making device used to provide audible alarms in a wide variety of devices including, for example, smoke detectors and medical equipment. Such devices can use a piezoelectric transducer and associated circuitry as a noise-making device. The transducer bends in response to an applied voltage. If an oscillating voltage is applied to the transducer at an appropriate rate, the flexing of the transducer produces an audible sound of substantial volume. An associated electrical circuit is used to apply the oscillatory voltage signal to the transducer.
U.S. Pat. No. 3,815,129, "Piezoelectric Transducer and Noise Making Device Utilizing Same," is incorporated by reference herein and describes an alarm device using a piezoelectric transducer. That patent shows a self-oscillating transducer employing a feedback circuit and requiring three external electrical connections (T.sub.1, T.sub.2, and T.sub.3) between the circuit and the transducer. U.S. Pat. No. 3,879,726, "Audible Alarm Unit," incorporated by reference herein, shows an audible alarm using a piezoelectric transducer, and having a separate printed circuit board 16 carrying the components of the electrical circuit used to operate the transducer. As can be seen in FIG. 1, the housing must be large enough to accommodate the transducer, the printed circuit board, and the electrical components.
Using a printed circuit board adds to the cost of material and labor. The board also inherently prevents the alarm unit from being further reduced in size. Both disadvantages are significant, since the applications of these alarm units require that they be as inexpensive as possible, and also frequently require them to be as small as possible, while still preserving the desired alarm characteristic.
Accordingly, the present invention provides a transducer and electrical circuit assembly which greatly reduces the cost of material and labor in manufacturing an alarm by eliminating the use of a printed circuit board and the necessary external third terminal normally required in a self-oscillating piezoelectric transducer when using a separate, external circuit board.